Polyurethane plastics



rates ware No Drawing. Filled Au 1, 1957, Ser. No. 675,538 Claimspriority, application Germany Nov. 16, 1956 3 Claims. (Cl. 26047) Thisinvention relates generally to the manufacture of polyurethane plasticsand, more particularly, to a novel and improved method for makinghomogeneous polyurethane plastics and to the improved product resultingtherefrom.

It has been proposed heretofore to manufacture high molecular weightcross-linked plastics by reacting a linear o substantially linearcondensation or polymerizationproduct containing at least two reactivehydrogen atoms and having a molecular Weight of at least about 1,000with an organic polyisocyanate and a cross-linker or chain extenderwhich may be a compound having a molecular weight of less than 1,000having at least two hydrogen atoms which will react With an organicisocyanate. The condensation or polymerization product used in suchreactions is an organic compound having at least two reactive hydrogenatoms and may be a polyester, a polyester amide, polyalkylene etherglycol, a polythioether glycol, a polyacetal or the like having amolecular Weight of at east 1,000. The cross-linking agent or compoundmay be any suitable compound having reactive hydrogen atoms, such as,for example, water, dior trivalent alcohols, amino alcohols or diamines,and a molecular weight of less than 1,000.

One of the more suitable processes for making homogeneous polyurethaneplastics is disclosed in US. Patent 2,729,618, granted to Muller et a1.January 3, 1956. In accordance with the process disclosed in the patent,the polyurethane plastic is prepared by reacting a polyester with anexcess of an organic polyisocyanate and reacting the resulting productwith a glycol. The glycol may be either an aliphatic compound or acyclic glycol, such as quinitol or hexahydropyrocatechol. By varying theamount of polyester, polyisocyanate or cross-linking agent used, thephysical characteristics of the resulting polyurethane plastic may bevaried from elastomeric or rubber-like to leather-like. The physicalcharacteristics of the plastic are not only determined by the properchoice of a cross-linking agent but also by the proper selection oforganic polyisocyanate and organic com pound having reactive hydrogenatoms. It has been found that when an aliphatic glycol, such as ethyleneglycol, is used as the cross-linking agent, polyurethane plastics havingthe more desirable physical characteristics are obtained only when1,5-naphthylene diisocyanate or para-phenylene diisocyanate is used. Inother words, it has been necessary heretofore to use 1,5-naphthylenediisocyanate in most formulations. This particular diisocyanate has thedisadvantages of being relatively expensive and diflicult to make.Moreover, the product obtained by reacting 1,5-naphthylene diisocyanatewith the organic compound having at least two reactive hydrogen atomscannot be stored for any appreciable time before it is cast into thedesired configuration because it becomes too viscous and cannot bepoured into the casting mold.

It is possible to substitute organic polyisocyanates of less chemicalreactivity than that of 1,5-naphthylene diisocyanate if a glycolcontaining at least two condensed aromatic rings is used as thecross-linker. The organic 1 tent having at least two reactive hydrogenatoms.

polyisocyanates having this reduced chemical reactivity include4,4-diphenylmethane diisocyanate, 2,4-toluylene diisocyanate and thelike. Processes which involve the use of glycols having at least twocondensed aromatic rings have the disadvantage, however, of beingdifficult to control because such glycols have a high melting point andrelatively low solubility and the processes are not especially adaptablefor preparing cast polyurethane products. It is very difficult toproduce homogeneous melts by such processes and operation at relativelyhigh temperatures is required with the result that the time intervalbetween preparation of the plastic mass and final casting is relativelyshort, making it impossible to devise an uncomplicated castingprocedure.

It is therefore an object of this invention to provide an improvedprocess for making elastomeric polyurethane plastics devoid of theforegoing disadvantages. Another object of the invention is to provide amethod for making polyurethane plastics from organic compounds having atleast two reactive hydrogen atoms and a molecular weight of at least1,000, organic polyisocyanates and an improved.

cross-linking agent which permits use of those'organic polyisocyanateswhich have a chemical reactivity with reactive hydrogen atoms less thanthat of 1,5-naphthylene diisocyanate. Still another object of theinvention is to provide a method for making elastomeric polyurethaneplastics from the organic polyisocyanates having a chemi-.

cal reactivity less than that of 1,5-naphthylene diisocyanate havingimproved physical characteristics. A further object of the invention isto provide a method for making a storage-stable isocyanate-modifiedorganic compound Still a further object of the invention is to provide anovel polyurethane plastic.

Generally speaking, the foregoing objects as well as others areaccomplished in accordance with this invention by providing a method forpreparing homogeneous or non-porous polyurethane plastics from anorganic polyisocyanate, an organic compound having at least two reactivehydrogen atoms and a molecular Weight of at least 1,000 and aphenylene-di(B-oxyethylether). It has been found that cross-linkednon-porous polyurethane plastics having suitable elastomeric orleather-like charthat of 1,5-naphthylene diisocyanate provided that aphenylene-di({3-oxyethylether) is used as the cross-linking agentinstead of one of the heretofore available glycols, diamines, water orother cross-linking agents. The organic compound having at least tworeactive hydrogen atoms and a molecular Weight of at least 1,000 musthave an hydroxyl number of from about 20 to about in order to produce aplastic having the desirable rubber-like characteristics. excess oforganic polyisocyanate over that required to react with all of thereactive hydrogen atoms of the organic compound having at least tworeactive hydrogen atoms. The preferred ratio of organicpolyisocyanate toorganic compound having reactive hydrogen atoms is from about 2.5 toabout 4 mols organic polyisocyanate per mol of organic compound havingat least two reactive hydrogen atoms although from about 2 mols to about6. mols organic polyisocyanate per mol of organic compound having atleast two reactive hydrogen atoms may be utilized.

The product obtained in accordance with this invention has a structurecontaining the following grouping:

' wherein R is a divalent radical derived from an aromatic It ispreferred to use a molar J poiyisocyanate and R is the residue of asubstantially linear organic compound having at least two reactivehydrogen atoms and a molecular weight of at least 1,000.

Substitution of a phenylene-di(fi-oxyethylether) for one of theheretofore available linear aliphatic or cyclic glycols provides aunique process inasmuch as it permits the use of the lesser reactiveorganic polyisocyanate, such as, for example, 4,4'-diphenylmethanediisocyanate instead of 1,5-naphthylene diisocyanate without anysubstantial sacrifice in physical characteristics in the product. Themelting point of the phenylene-di(B-oxyethylethers) is about 100 C. andeach of these ethers is soluble in the reaction mixture normally usedfor making polyurethane plastics permittingv processing of the plasticmass at low temperatures. The novel cross-linker provided by thisinvention has the further advantage of being more soluble in theprepolymer formed by the reaction of the organic compound having atleast two reactive hydrogen atoms with the organic polyisocyanate thanthe heretofore available cross-linkers. The time interval between mixingthe cross-linker with the prepolymer and hardening of the mixture to thepoint where it can no longer be poured or molded is considerably longerthan the time interval when 1,5-naphthylene diisocyanate and one of thelinear aliphatic or cyclic glycols is used, thus providing a processadaptable to continuous production and more suitable for combining withother processing steps.

Any suitable phenylene-di(B-oxyethylether) may be utilized as thecross-linking agent or chain extender in accordance with this invention,but it is preferred to use paraphenylene-di(B-oxyethylether). Othersuitable phenylene-di(B-oxyethylethers) include the isomers andalkylsubstituted products, such as, for example,meta-phenylene-di(fl-oxyethylether), ortho-phenylenedi(,8-oxyethylether), methyl-p-phenylene-di(B-oxyethylether) and thelike. One of the novel cross-linking agents may be used alone or inadmixture with each other or in admixture with any other suitable diorpolyvalent polyalcohol having aliphatic or aromatic ring systems, suchas, for example, ethylene glycol, diethylene glycol, 1,4-butanediol,1,3-propylene diol, trimethylol propane, a di-primary aromatic diamineof the type disclosed in U.S. Patent 2,778,- 810, hexahydropyrocatecholor the like. From about 0.4 to about 4 mols of thephenylene-di(B-oxyethylether) and, preferably, from about 1.5 to about2.5 mols phenylenedi(,8-oxyethylether) per mol organic compound havingat least two reactive hydrogen atoms and a molecular weight of at least1,000 should be used.

Any suitable organic compound having at least two reactive hydrogenatoms and a molecular weight of at least 1,000 and, preferably, such acompound having terminal hydroxyl groups may be utilized. A polyester orpolyester amide prepared by condensation of a dicarboxylic acid, suchas, for example, succinic acid, adipic acid, sebacic acid, or phthalicacid, with a glycol, such as, for example, ethylene glycol, diethyleneglycol, 1,2-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol,with or without the addition of amino alcohols, amino carboxylic acidsor diamines may be used. Preferably an excess of glycol is used'in orderthat the polyester will have terminal OH groups. Furthermore, apolyether or polythioether, such as, for example, a polyalkylene etherglycol prepared by condensation of propylene oxide or ethylene oxide ora polyalkylene ether glycol, prepared by polymerizing tetrahydrofuran, apolyacetal of formaldehyde, or the like are further examples of suitableorganic compounds having at least two reactive hydrogen atoms and amolecular weight of at least 1,000. The polythioethers may have SHgroups instead of or in combination with OH groups. As statedhereinbefore, the hydroxyl numher of the hydroxyl containing organiccompoundhaving 1,000 should contain from about 0.6 to about 2.4%functional groups, e.g., hydroxyl groups.

As pointed out hereinbefore, the organic polyisocyanates heretoforeconsidered unsuitable for making elastomeric polyurethane plastics ofoptimum physical characteristics may be utilized in accordance with thisinvention. Examples of such organic polyisocyanates include4,4'-diphenylmethane diisocyanate, alkyl-substituted 4,4-diphenylmethane diisocyanates, such as, for example,diphenyldimethylmethane-4,4'-diisocyanates and the like, 2, fi-toluylenediisocyanate, mixtures of 2,6-toluylene diisocyanate and 2,4-toluylenediisocyanate, m-phenylene diisocyanate, and uretdione containingdiisocyanates. Moreover, those more reactive organic diisocyanates suitable for use with the heretofore available cross-linking agents may, ofcourse, be used, such as, for example, 1,5- naphthylene diisocyanate,p-phenylene diisocyanate or any other suitable organic polyisocyanate.

Homogeneous or non-porous polyurethane plastics having the mostdesirable physical characteristics are obtained when diisocyanates andpredominantly linear organic compounds having reactive hydrogen atomsand a molecular weight of at least 1,000 are used, so diisocyanates anddifunctional polyesters, polyalkylene ethers and the like are preferred.

In practicing the invention, the organic compound having at least tworeactive hydrogen atoms and a molecular weight of at least 1,000 may bereacted with an excess of organic diisocyanate over that required toreact with each of the reactive hydrogen atoms in the terminal groups toform aprepolymer or adduct having terminal NCO groups and a highermolecular weight. This reaction should be conducted under substantiallyanhydrous conditions and the resulting prepolymer may then be reactedwith the phenylene-di(fi-oxyethylether) to form the cross-linkedpolyurethane plastic. This procedure gives best results, producing aproduct of optimum physical characteristics. However, it is possible tomix the phenylene-di(fi-oxyethylether) with the organic compound havingat least two reactive hydrogen atoms and a molecular weight of at least1,000 and to mix this mixture with the organic polyisocyanates. Each ofthese procedures is suitable for use in preparing polyurethane plasticsby a casting process wherein the mixture of prepolymer and cross-linkingagent is poured as a liquid into a mold and heated until a hardened orsolidified product is obtained. Solidification can be retarded by theaddition of small amounts of acids or acid chlorides or tertiary bases.

In accordance with another embodiment of the invention particularly wellsuited for making polyurethane plastics by a two-step process in whichthe second step may be separated for a considerable length of time fromthe first step, the organic compound having at least two reactivehydrogen atoms and a molecular weight of at least 1,000 is mixed withless than the theoretical amount of organic polyisocyanate required toreact with all of the reactivehydrogen'atoms thereof and chemicalreaction is brought about. This product is then stored until it isdesired to form the finished polyurethane plastic at which time thephenylene-di(fi-oxyethylether) and additional organic polyisocyanate areadded and chemical reaction is brought about to complete the formationof plastic. This procedure may be modified to the extent that theorganic compound having at least two reactive hydrogen atoms is reactedwith an excess of organic polyisocyanate over that required to reactwith all of the terminal reactive hydrogen atoms and an excess ofphenylenedi(B-oxyethylether) over the amount required to react with allof the isocyanate groups present may be added. When preparingapolyurethane plastic in a two step process the first step is built up byusing less than the theoretical amount of organic polyisocyanatepreferably -99% calculated on the end groups of the available reactivehydrogen atoms. When it is desired to produce the final product,additional polyisocyanate may be added and chemical reaction broughtabout.

The ratios of organic polyisocyanate to organic compound having at leasttwo reactive hydrogen atoms and of phenylene-di(fl-oxyethylether) toprepolymer should be carefully controlled depending upon the particularphysical characteristics desired in the finished product. Thus, forexample, when 4,4-diphenylmethane diisocyanate andp-phenylene-di(B-oxyethylether) are used together, an excess of fromabout 200% to about 400% organic diisocyanate over that required toreact with the reactive hydrogen atoms of the organic compound willproduce a polyurethane plastic which is relatively hard and elastic. Infact, the plastic produced by this process having a given hardness ismore elastic than the plastics heretofore available. If less than 200%excess diisocyanate is used, a softer and more rubber-like plastichaving improved tensile strength, tear resistance, elongation andelasticity is obtained. The following table demonstrates the change inhardness and elasticity when a given polyester (of Example 1) isprocessed withincreasing amounts of 4,4-diphenyl methanediisocyanate andpphenylene-di B-oxyethylether) Isocyanate, Ether, Hardness, Elasticity,percent percent degrees percent Shore The novel elastomeric homogeneousor non-porous polyurethane plastics provided by this invention may beused for making various rubber-like articles of manufacture, such as,for example, bushings, gears, door latches for vehicles, automobiletires and the like.

Example 1 Into 200 g. of a glycol adipic acid polyester dehydrated at130 C., with an OH number of 53, 70 g. 4,4'-diphenylmethane diisocyanateare stirred in at the same temperature. The temperature is maintained at130140 C. for 15 minutes and then allowed to cool to 100 C. After briefapplication of vacuum, 33.6 g. molten p-phenylene di(,8-hydroxyethylether) are stirred in at this temperature and the homogeneous melt ispoured into molds. In about 1% minutes the clear melt suddenly becomescloudy and after about more minutes solidification occurs. After 24hours postcure at 100 C. an elastic material with the followingproperties is obtained:

Under the same reaction conditions, on using the following proportions:200 g. glycol adipic acid polyester (OH number 53) 80 g.4,4'-diphenylmethane diisocyanate, and 40 g.p-phenylene-di(ti-hydroxyelhyl ether), products with the followingproperties are obtained:

260 kg./cm.

Strength Elongation 430%. Permanent set 240%.

Load at 300% elongation 141 kg./cm. Hardness 93 Shore. Elasticity 39%With the following starting materials: 200 g. glycol adipic acidpolyester (OH number 53), 70 g. 4,4'-diphenylmethane diisocyanate, and33.6 g. m-phenylene-diqi-hyp-phenylene-di- (fl-hydroxyethyl ether).

droxyethyl ether), under the previously specified reaction conditions,materials with the following properties result:

Strength 193 kg./crn. Elongation 490%. Permanent set 16%.

Load at 300% elongation 115 kg./cm. Hardness 85 Shore. Elasticity 35%.

From the following starting materials: 200 g. tetrahydrofuranpolymerizate (OH number 37), 70 g. 4,4-dIphenyl- ,methane diisocyanate,and 33.6 g. p-phenylene-di(;3-hydroxyethyl ether), under the conditionsspecified above, a product with the following properties is given:

Strength 195 kg./cm. Elongation 495%. Permanent set 46%.

Load at 300% elongation 137 l g./cm. Hardness 94 Shore. Elasticity 49%.

When 200 g. glycol adipic acid polyester (OH number 53), 60 g.rn-phenylene diisocyanate, and 49.6 g. pphenylene-di(ti-hydroxyethylether), are processed in the initially described way, an elastomericmaterial with the following properties is obtained:

into 1,000 g. of a glycol adipic acid ester with an OH number 53,dehydrated at 130 C., are stirred 47.5 g.

After a homogeneous melt has formed, 175 g. 4,4-diaminodiphenylmethanediisocyanate are added gradually at 90100 C. Thereupon, it is stirreduntil a high viscosity melt results which, poured into sheets, ispostcured 12 hours at 100 C. The material obtained can be drawn out to asheet on the roller and after rolling in 8% toluylene diisocyanate dimercan be pressed into molded bodies which have the following mechanicalproperties:

. Strength 314 kg./cm.

Elongation 682%. Permanent set 11%.

Load at 300% elongation 38 kg./crn.

Hardness 75 Shore.

Elasticity 44%.

Tear 40 kg.

Example 3 Into 200 g. of a tetrahydrofuran polymerizate with an OHnumber of 50, g. of 4,4'-diphenylmethane diisocyanate are stirred afterdehydration at C./ 12 mm. The temperatureincreases to 138 C. It isheated 20 minutes more at 130 C. and then 40 g. of previously meltedpphenylene-ddihydroxyethyl ether'are added to the melt. It is pouredinto prepared molds and kept at 100 C. for 24 hours more. An elastomericmaterial with the following mechanical properties results:

Strength kg./cm. Elongation 495%. Permanent set 56%. Elasticity 49%.Hardness 94 Shore. Load at 300% elongation 137 kg./cm.

Example 4 Into 300 g. of a polythioether produced by self-condensationof thiodiglycol, with an OH number of 4-5, are stirred 95 g.4,4-diphenylmethane diisocyanate after dehydration at 130 C. Thereaction mixture is kept at this temperature for IO'minutes and then37.2 g. of previously melted vp-phenylene-,8-dihydroxyethyl ether areadded. After good stirring it is poured into prepared forms, heated for24 hours at 100 C. and an elastomeric material with the followingproperties is obtained:

Strength 146 kg./cm.

Elongation 250%.

Permanent set 26%.

Elasticity 44%.

Hardness 87 Shore.

Example 5 noniozo -oonnon Although the invention has been described inconsiderable cletail in the foregoing for the purpose of illustration,it is to be understood that such detail is solely for this purpose andthat variations can be made by those skilled in the art Withoutdeparting from the spirit and scope of he invention except as is setforth in the claims.

What is claimed is:

1. A method for making an elastomeric substantially non-porouspolyurethane which comprises reacting a member selected from the groupconsisting of a polyester prepared by esterification of a dicarboxylicacid and a saturated glycol, a poly(alkylene ether) glycol, apolythioether glycol having 0 and S ether links in the chain thereof,and a polyacetal prepared from a glycol and formaldehyde, said groupmember having an hydroxyl number of from about 20 to about 80, amolecular Weight of at least about 1000 and an acid number notsubstantially greater than about 1.5, p-phenylene di(fi-hydroxyethylether) in the ratio of from about 0.4 mol to about 4 mols per molof said group member, and a member selected from the group consisting of4,4-diphenyl dimethyl methane diisocyanate and 4,4'-diphenyl methanedilsocyanate in an amount in excess of at least about 2 mols thereof permol of said first mentioned group member.

2. The product of the process of claim 1.

3. The process of claim 1 wherein the diisocyanate is 4,4'-diphenylmethane diisocyanate.

References Cited in the file of this patent UNITED STATES PATENTS2,729,618 Miiller Jan. 3, 1956 2,861,972 Muller Nov. 25, 1958 FOREIGNPATENTS 519,014 Belgium Oct. 5, 1953 167,675 Australia May 14, 19561,128,561 France Aug. 27, 1956 755,779 Great Britain Aug. 29. 1956 OTHERREFERENCES Bayer: Angewandte Chemie, 59, 257-272 (1947).

1. A METHOD FOR MAKING AN ELASTOMIC SUBSTANTIALLY NON-POROUSPOLYURETHANE WHICH COMPRISES REACTING A MEMBER SELECTED FROM THE GROUPCONSISTING OF A POLYESTER PREPARED BY ESTERIFICATION OF A DICARBOXYLICACID AND A SATUREATED GLYCOL, A POLY(ALKYLENE ETHER) GLYCOL, APOLYTHIOETHER GLYCOL HAVING O AND S ETHER LINKS IN THE CHAIN THEREOF,AND A POLYACETAL PREPARED FROM A GLYCOL AND FORMALDEHYDE, SAID GROUPMEMBER HAVING AN HYDROXYL NUMBER OF FROM ABOUT 20 TO ABOUT 80, AMOLECULAR WEIGHT OF AT LEAST ABOUT 1000 AND AN ACID NUMBER NOTSUBSTANTIALLY GREATER THAN ABOUT 1,5, P-PHENYLENE DI-(B-HYDROXYETHYLETHER) IN THE RATIO OF FROM ABOUT 0.4 MOL TO ABOUT 4 MOLS PER MOLOF SAID GROUP MEMBER , AND A MEMBER SELECTED FROM THE GROUP CONSISTINGOF 4,4''-DIPHENYL DIMETHYL METHANE DIISOCYANATE AND 4,4''-DIPHENYLMETHANE DIISOCYANATE IN AN AMOUNT IN EXCESS OF AT LEAST ABOUT 2 MOLSTHEREOF PER MOL OF SAID FIRST MENTIONED GROUP MEMBER.